In cold environments, a person's hands and feet will typically get cold first. Accordingly, a variety of lined gloves and boots are available for people performing activities in cold-air environments. In addition, commercially-available chemical hand and foot warmers can be inserted into one's gloves and/or boots. These hand and foot warmers are small gas-permeable pouches that contain particles of materials that generate an exothermic reaction in the presence of oxygen. The active ingredient in many of these products is iron “particles” (e.g., shavings, filings and/or powder) that provide a heating source through a process of accelerated rust. That is, the iron particles oxidize in the presence of oxygen to produce iron oxide. This reaction is exothermic and lasts for several hours as long as there is a steady supply of oxygen as is the case in the ambient air environment. Most gloves and boots allow for sufficient air infiltration to maintain this exothermic reaction.
In underwater environments, divers wear wetsuits or drysuits that cling to one's skin thereby minimizing any air space between the diver and the suit. Furthermore, the underwater environment does not have a ready supply of oxygen. Accordingly, the above-described commercially-available hand and foot warmers are of no value to an underwater diver.